The present invention relates to semiconductor processing.
The fabrication of modern semiconductor device structures has traditionally relied on plasma processing in a variety of operations such as etching, depositing or sputtering. Plasma etching involves using chemically active atoms or energetic ions to remove material from a substrate. Plasma Enhanced Chemical Vapor Deposition (PECVD) uses plasma to dissociate and activate chemical gas so that the substrate temperature can be reduced during deposition. Plasma sputtering also deposits materials onto substrates, where plasma ions such as argon impact a material surface and sputter the material that is then transported as neutral atoms to a substrate. Additional plasma processes include plasma surface cleaning and physical-vapor deposition (PVD) of various material layers.
Conventionally, plasma is generated using a radio frequency powered plasma source. In a xe2x80x9ctypicalxe2x80x9d radio frequency powered plasma source, alternating current (AC) power is rectified and switched to provide current to an RF amplifier. The RF amplifier operates at a reference frequency (13.56 MHz, for example), drives current through an output-matching network, and then through a power measurement circuit to the output of the power supply. The output match is usually designed to be connected a generator that is optimized to drive particular impedance such as 50 ohms, in order to have the same characteristic impedance as the coaxial cables commonly used in the industry. Power flows through the matched cable sections, is measured by the match controller, and is transformed through the load match. The load match is usually a motorized automatic tuner, so the load match operation incurs a predetermined time delay before the system is properly configured. After passing through the load match, power is then channeled into a plasma excitation circuit that drives two electrodes in an evacuated processing chamber. A processing gas is introduced into the evacuated processing chamber, and when driven by the circuit, plasma is generated. Since the matching network or the load match is motorized, the response time from the matching network is typically in the order of one second or more.
Conventionally, plasma is continuously generated in order to obtain the large amount of power necessary to deposit the layers at high speed and thereby to improve the shapes of stepped parts thereof (coverage). As noted in U.S. Pat. No. 5,468,341 entitled xe2x80x9cPlasma-etching method and apparatus thereforxe2x80x9d, the amount of ion energy reaching a surface of the object to be etched in conventional RF sources can be accomplished by controlling the power of RF waves, the controllable range of dissociation process in plasmas is narrow and, therefore, the extent of controllable etching reactions on the surface of the object wafer is narrowly limited. Also, since the magnetic fields are present in a plasma generation chamber for high-density plasmas, a magnetohydrodynamic plasma instability can exist due to, for example, drift waves generated in the plasmas, which leads to a problem wherein the ion temperature rises and the directions of ion motions become nonuniform. Further, the problems include a degradation of a gate oxide film and a distortion of etching profile due to the charges accumulated on the wafer.
In a deposition technology known as atomic layer deposition (ALD), various gases are injected into the chamber for about 100-500 milliseconds in alternating sequences. For example, a first gas is delivered into the chamber for about 500 milliseconds and the substrate is heated, then the first gas (heat optional) is turned off. Another gas is delivered into the chamber for another 500 milliseconds (heat optional) before the gas is turned off. The next gas is delivered for about 500 milliseconds (and optionally heated) before it is turned off. This sequence is done for until all gases have been cycled through the chamber, each gas sequence forming a mono-layer which is highly conformal. ALD technology thus pulses gas injection and heating sequences that are between 100 and 500 milliseconds. This approach has a high dissociation energy requirement to break the bonds in the various precursor gases such as silane and oxygen and thus requires the substrate to be heated to a high temperature, for example in the order of 600-800 degree Celsius for silane and oxygen processes.
In one aspect, an apparatus to perform semiconductor processing includes a process chamber; a flash lamp adapted to be repetitively triggered; and a controller coupled to the control input of the flash lamp to trigger the flash lamp.
Implementations of the above aspect may include one or more of the following. The flash lamp can be pulsed to perform atomic layer processing, which includes one or more of the following: deposition, etching, epitaxial deposition, and sputter deposition. A solid state plasma generator employing frequency tuning can be used to achieve output matching. The plasma generator can be a solid state generator without any moving parts and having a short tuning response time. The solid state generator includes: a switching power supply; an amplifier coupled to the power supply; a reference frequency generator coupled to the amplifier; a power measurement circuit providing feedback to a comparator and to the reference frequency generator; an output match section coupled to the power measurement circuit; and a plasma excitation circuit coupled to the output match section. A plurality of precursor inlets can be coupled to the chamber, and the precursor from the precursor inlets reacts when the flash lamp is triggered. The controller can be computer controlled or can be a hardwired circuit. The controller turns on the flash lamp in an atomic layer process. The controller can cycle the flash lamp multiple times to perform atomic layer processing in the process chamber. The multiple layers can be plasma-assisted layers and non plasma-assisted layers.
In another aspect, a method to deposit multi-layer films on a semiconductor includes introducing a gas into a processing chamber; and triggering a flash lamp to generate thermal energy in the chamber to deposit a layer.
Implementations of the aspect may include one or more of the following. The method includes purging the chamber and then sequentially pulsing the flash lamp for each layer to be deposited.
In yet another aspect, a multi-layer semiconductor processing chamber includes a gas source coupled to the chamber for introducing a processing gas into a reaction chamber having a sample disposed therein; a high intensity flash lamp coupled to the chamber to react the processing gas; and a controller coupled to the flash lamp to trigger the flash lamp for each deposited layer.
Implementations of the above aspect may include one or more of the following. A solid state RF plasma source can be used in conjunction with the flash lamp, the source including: switching power supply; an RF amplifier coupled to the power supply; a reference frequency generator coupled to the RF amplifier; a power measurement circuit providing feedback to a comparator and to the reference frequency generator; an output match section coupled to the power measurement circuit; and a plasma excitation circuit coupled to the output match section. The controller triggers the flash lamp and/or pulses the solid state RF plasma source. The controller sequentially triggers the flash lamp and/or pulses the solid state RF plasma source for each layer to be deposited.
Advantages of the system may include one or more of the following. The system can instantaneously deliver a significant amount of energy to the wafer surface to initiate a desirable surface reaction. The system can perform a combination of pulsed plasma and/or flash heating to thermally activate chemical precursors on the surface of the substrate at temperatures slightly below that required to initiate a sustained thermal reaction. This technique can be used to build extremely thin layers of material for Atomic Layer Deposition processes. The system offers better control thickness. Customer can use thinner films to achieve the same result, thereby extending Moore""s law. The resulting high quality films possess superior properties such as high uniformity, controlled resistivity, high diffusion resistance, and high conformality, among others. The system thus enables high precision etching, deposition or sputtering performance. The pulse modulation of a flash bulb and/or a radio frequency powered plasma source enables a tight control the radical production ratio in plasmas, the ion temperature and the charge accumulation. Also, since the time for accumulation of charges in a wafer is on the order of milli-seconds, the accumulation of charges to the wafer is suppressed by the pulse-modulated plasma on the order of micro-seconds, and this enables the suppression of damage to devices on the wafer caused by the charge accumulation and of notches caused during the electrode etching process. The system allows the substrate be heated to a relatively low temperature, typically less than 400 degrees Celsius. The processing of the wafer at lower temperatures can reduce the thermal budget and can be advantageous in reducing thermally induced mechanical stresses, diffusion alloying of adjacent layers within the substrate, and minimizing grain growth, among others.
Other advantages may include one or more of the following. The system attains highly efficient plasma operation in a compact substrate process module that can attain excellent characteristics for etching, depositing or sputtering of semiconductor wafers as represented by high etch rate, high uniformity, high selectivity, high anisotropy, and low damage. The system achieves high density and highly uniform plasma operation at low pressure for etching substrates and for deposition of films on to substrates. Additionally, the system is capable of operating with a wide variety of gases and combinations of gases, including highly reactive and corrosive gases.